1. Field of Invention
The present invention relates to a switching regulator with transient control function and a control circuit and a method therefor.
2. Description of Related Art
There are various types of switching regulators, such as buck converter, boost converter, inverter converter, buck-boost converter and so on. The foregoing circuits can also be categorized into synchronous type and asynchronous type; a synchronous switching regulator employs two power transistor switches (the buck-boost converter employs four power transistor switches), while in an asynchronous switching regulator one of the power transistor switches is replaced by a diode. Taking a synchronous buck converter for example, its circuit structure is shown schematically in FIG. 1. The buck converter 1 includes two power transistor switches Q1 and Q2 controlled by a control circuit 10. The control circuit 10 generates a switch control signal according to a feedback signal FB generated from an output terminal Vout, to control the operation of the power transistor switches Q1 and Q2 such that power is transmitted from an input terminal Vin to an output terminal Vout. FIG. 2 shows a boost converter 2; FIG. 3 shows an inverter converter 3; FIG. 4 shows a buck-boost converter 4; FIG. 5 shows an asynchronous buck switching regulator 1′; and FIG. 6 shows an asynchronous boost switching regulator 2′. Although the foregoing circuits have different circuit structures and different numbers of power transistor switches, they all convert power from the input terminal Vin to the output terminal Vout by controlling the power transistor switches with the switch control signals generated by the control circuit 10 according to the feedback signal FB.
There are two types of feedback control mechanisms employed in the foregoing switching regulators: voltage mode and current mode. However, in either mode, when the load current changes abruptly, it will cause output voltage overshoot or undershoot, generating a larger ripple at the output terminal as shown in FIG. 7.
In view of the drawback of the foregoing prior art, the present invention provides a switching regulator with transient control function and a control circuit and a method therefor to improve the transient response and reduce the voltage ripple.